org.apache.commons.logging

Class LogFactory

Known Direct Subclasses:
Log4jFactory, LogFactoryImpl

public abstract class LogFactory
extends java.lang.Object

Factory for creating Log instances, with discovery and configuration features similar to that employed by standard Java APIs such as JAXP.

IMPLEMENTATION NOTE - This implementation is heavily based on the SAXParserFactory and DocumentBuilderFactory implementations (corresponding to the JAXP pluggability APIs) found in Apache Xerces.

Version:
$Revision: 1.27 $ $Date: 2004/06/06 21:15:12 $
Authors:
Craig R. McClanahan
Costin Manolache
Richard A. Sitze

Field Summary

static String
FACTORY_DEFAULT
The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.
static String
FACTORY_PROPERTIES
The name of the properties file to search for.
static String
FACTORY_PROPERTY
The name of the property used to identify the LogFactory implementation class name.
protected static String
SERVICE_ID
JDK1.3+ 'Service Provider' specification.
protected static Hashtable
factories
The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.

Constructor Summary

LogFactory()
Protected constructor that is not available for public use.

Method Summary

private static void
cacheFactory(ClassLoader classLoader, LogFactory factory)
abstract Object
getAttribute(String name)
Return the configuration attribute with the specified name (if any), or null if there is no such attribute.
abstract String[]
getAttributeNames()
Return an array containing the names of all currently defined configuration attributes.
private static LogFactory
getCachedFactory(ClassLoader contextClassLoader)
Check cached factories (keyed by contextClassLoader)
protected static ClassLoader
getContextClassLoader()
Return the thread context class loader if available.
static LogFactory
getFactory()
Construct (if necessary) and return a LogFactory instance, using the following ordered lookup procedure to determine the name of the implementation class to be loaded.
abstract Log
getInstance(Class clazz)
Convenience method to derive a name from the specified class and call getInstance(String) with it.
abstract Log
getInstance(String name)
Construct (if necessary) and return a Log instance, using the factory's current set of configuration attributes.
static Log
getLog(Class clazz)
Convenience method to return a named logger, without the application having to care about factories.
static Log
getLog(String name)
Convenience method to return a named logger, without the application having to care about factories.
private static InputStream
getResourceAsStream(ClassLoader loader, String name)
protected static LogFactory
newFactory(String factoryClass, ClassLoader classLoader)
Return a new instance of the specified LogFactory implementation class, loaded by the specified class loader.
abstract void
release()
Release any internal references to previously created Log instances returned by this factory.
static void
release(ClassLoader classLoader)
Release any internal references to previously created LogFactory instances that have been associated with the specified class loader (if any), after calling the instance method release() on each of them.
static void
releaseAll()
Release any internal references to previously created LogFactory instances, after calling the instance method release() on each of them.
abstract void
removeAttribute(String name)
Remove any configuration attribute associated with the specified name.
abstract void
setAttribute(String name, Object value)
Set the configuration attribute with the specified name.

Field Details

FACTORY_DEFAULT

public static final String FACTORY_DEFAULT
The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.

FACTORY_PROPERTIES

public static final String FACTORY_PROPERTIES
The name of the properties file to search for.

FACTORY_PROPERTY

public static final String FACTORY_PROPERTY
The name of the property used to identify the LogFactory implementation class name.

SERVICE_ID

protected static final String SERVICE_ID

factories

protected static Hashtable factories
The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.

Constructor Details

LogFactory

protected LogFactory()
Protected constructor that is not available for public use.

Method Details

cacheFactory

private static void cacheFactory(ClassLoader classLoader,
                                 LogFactory factory)

getAttribute

public abstract Object getAttribute(String name)
Return the configuration attribute with the specified name (if any), or null if there is no such attribute.
Parameters:
name - Name of the attribute to return

getAttributeNames

public abstract String[] getAttributeNames()
Return an array containing the names of all currently defined configuration attributes. If there are no such attributes, a zero length array is returned.

getCachedFactory

private static LogFactory getCachedFactory(ClassLoader contextClassLoader)
Check cached factories (keyed by contextClassLoader)

getContextClassLoader

protected static ClassLoader getContextClassLoader()
            throws LogConfigurationException
Return the thread context class loader if available. Otherwise return null. The thread context class loader is available for JDK 1.2 or later, if certain security conditions are met.
Throws:
LogConfigurationException - if a suitable class loader cannot be identified.

getFactory

public static LogFactory getFactory()
            throws LogConfigurationException
Construct (if necessary) and return a LogFactory instance, using the following ordered lookup procedure to determine the name of the implementation class to be loaded.
  • The org.apache.commons.logging.LogFactory system property.
  • The JDK 1.3 Service Discovery mechanism
  • Use the properties file commons-logging.properties file, if found in the class path of this class. The configuration file is in standard java.util.Properties format and contains the fully qualified name of the implementation class with the key being the system property defined above.
  • Fall back to a default implementation class (org.apache.commons.logging.impl.LogFactoryImpl).

NOTE - If the properties file method of identifying the LogFactory implementation class is utilized, all of the properties defined in this file will be set as configuration attributes on the corresponding LogFactory instance.

Throws:
LogConfigurationException - if the implementation class is not available or cannot be instantiated.

getInstance

public abstract Log getInstance(Class clazz)
            throws LogConfigurationException
Convenience method to derive a name from the specified class and call getInstance(String) with it.
Parameters:
clazz - Class for which a suitable Log name will be derived
Throws:
LogConfigurationException - if a suitable Log instance cannot be returned

getInstance

public abstract Log getInstance(String name)
            throws LogConfigurationException
Construct (if necessary) and return a Log instance, using the factory's current set of configuration attributes.

NOTE - Depending upon the implementation of the LogFactory you are using, the Log instance you are returned may or may not be local to the current application, and may or may not be returned again on a subsequent call with the same name argument.

Parameters:
name - Logical name of the Log instance to be returned (the meaning of this name is only known to the underlying logging implementation that is being wrapped)
Throws:
LogConfigurationException - if a suitable Log instance cannot be returned

getLog

public static Log getLog(Class clazz)
            throws LogConfigurationException
Convenience method to return a named logger, without the application having to care about factories.
Parameters:
clazz - Class from which a log name will be derived
Throws:
LogConfigurationException - if a suitable Log instance cannot be returned

getLog

public static Log getLog(String name)
            throws LogConfigurationException
Convenience method to return a named logger, without the application having to care about factories.
Parameters:
name - Logical name of the Log instance to be returned (the meaning of this name is only known to the underlying logging implementation that is being wrapped)
Throws:
LogConfigurationException - if a suitable Log instance cannot be returned

getResourceAsStream

private static InputStream getResourceAsStream(ClassLoader loader,
                                               String name)

newFactory

protected static LogFactory newFactory(String factoryClass,
                                       ClassLoader classLoader)
            throws LogConfigurationException
Return a new instance of the specified LogFactory implementation class, loaded by the specified class loader. If that fails, try the class loader used to load this (abstract) LogFactory.
Parameters:
factoryClass - Fully qualified name of the LogFactory implementation class
classLoader - ClassLoader from which to load this class
Throws:
LogConfigurationException - if a suitable instance cannot be created

release

public abstract void release()
Release any internal references to previously created Log instances returned by this factory. This is useful in environments like servlet containers, which implement application reloading by throwing away a ClassLoader. Dangling references to objects in that class loader would prevent garbage collection.

release

public static void release(ClassLoader classLoader)
Release any internal references to previously created LogFactory instances that have been associated with the specified class loader (if any), after calling the instance method release() on each of them.
Parameters:
classLoader - ClassLoader for which to release the LogFactory

releaseAll

public static void releaseAll()
Release any internal references to previously created LogFactory instances, after calling the instance method release() on each of them. This is useful in environments like servlet containers, which implement application reloading by throwing away a ClassLoader. Dangling references to objects in that class loader would prevent garbage collection.

removeAttribute

public abstract void removeAttribute(String name)
Remove any configuration attribute associated with the specified name. If there is no such attribute, no action is taken.
Parameters:
name - Name of the attribute to remove

setAttribute

public abstract void setAttribute(String name,
                                  Object value)
Set the configuration attribute with the specified name. Calling this with a null value is equivalent to calling removeAttribute(name).
Parameters:
name - Name of the attribute to set
value - Value of the attribute to set, or null to remove any setting for this attribute

Copyright 2002-2004 The Apache Software Foundation.